Hydrocarbons are produced from a wellbore. The wellbore generally consists of a casing system and a production string. The term casing system is used because, during the drilling of the wellbore, a series of concentric casing runs will be used in the wellbore. For example, a wellbore may consist of surface casing, intermediate casing and final casing. The surface casing, as the name implies, is set near the surface and is used to avoid contamination with surface water sands and to ensure circulation within the wellbore during the initial drilling process. Intermediate casing is set after a certain point in the wellbore and is designed to keep the wellbore open while the drilling operation continues to the pay zone.
After the wellbore reaches the pay zone (formation where commercial quantities of hydrocarbon may be produced) the final casing will be set. In all cases the casing extends from the surface to the “end” of the casing. The well is now cleaned and is ready to be produced. Piping and valves that are directly connected to the final casing will be installed at the surface, and a “production string” will be installed. The production string terminates in valves at the surface and passes into flow lines (production piping) and onto the remainder of the gathering system. Thus, between the pay zone and the surface, there will be two “pipes”, the production tubing and the “final” casing: the area between the inside of the casing and the production tubing is called the annulus.
Produced hydrocarbons generally flow only through the production string that is in contact through perforations in the casing with the pay zone. (There are some circumstances in gas wells where gas is produced through the annulus.)
Raw hydrocarbons (crude oil and natural gas) are not a refined product and contain many impurities that are removed during the refining process. Generally these impurities will cause buildup and corrosion all piping that come in contact with the unrefined (crude) hydrocarbon fluid. (There are exceptions where a crude fluid is well behaved and causes few problems in production piping.)
Corrosion and buildup will take place in the production tubing, the surface flow lines and the gathering system. Buildup can be scale (precipitates of minerals found in crude) and paraffin (a natural element found in crude). Corrosion finally causes failure of the piping system, often with disastrous effects; whereas, buildup slowly reduces the production. The industry controls these problems using various methods.
In the case of corrosion, chemical inhibitors are injected into production piping at the surface. This does little to help the production tubing, but the tubing may be replaced when necessary.
In the case of scale and paraffin, chemical inhibitors are injected into production tubing at the surface, but again the production tubing is not protected. Paraffin buildup can be removed by hot-oil washing the affected piping, including the production tubing.
Hot oil washing or treatment causes disruption of production and is expensive. Like hot oil washing, chemical inhibitors are expensive. Thus, there remains a need to reduce or eliminate corrosion and buildup in hydrocarbon piping.
The prior art shows a number of devices and/or systems where fluids are passed over a metal alloy or passed over a metal at some electric potential. The art shows that some reduction in scale and corrosion occurs. One of the early patent that recognized the potential for metal alloys to clean (or stabilize) produced fluids may be found in the disclosures of Mills, U.S. Pat. No. 1,608,709 and Craft et al., U.S. Pat. No. 3,448,034. Walker, U.S. Pat. No. 4,789,031, and Rippetoe et al., U.S. Pat. No. 5,485,833 disclose the use of a metal alloy to reduce buildup and reference other prior art using metals and metal alloys. These devices reduce the effects of buildup and corrosion, but require that the device be installed at the bottom of or in the production string. See also the design patent of the inventors D446,797 (Melton et al.) that discloses a unique design to maximize contact between the produced fluid and a metal alloy.
Installation of the Mills, Craft, Walker, Rippetoe and Melton et al. devices requires removal and reinstallation of the production string or installation of the device from the beginning. Pulling a production string is an expensive process and is often not economic in a marginal or stripper well. After the passage of time, the actual alloy tends to cake over and the effectiveness of the alloy is reduced, requiring that the alloy be cleaned. Thus, an economic method and device for reducing buildup and corrosion in surface piping is required that is readily maintained and assures turbulent flow over the alloy.
In a similar manner, surface piping for water may experience corrosion and scaling. It is known that metal alloys and in particular the Walker Alloy will reduce scale and corrosion. In fact Case, U.S. Pat. No. 851,159 recognized the use of metal compounds for removing Boiler-Scale. A product utilizing the Walker/Craft alloy was sold in the United States as early as 1993 under the trade name “Emissions Panther Water Stabilizer” for use with water. Other products were offered in early 1999 under the brand name “Da-Gator” for use with water. In fact, a Federal Mark (s/n 75/751870) claiming use in commerce on Jul. 2, 1999 was filed for on Jul. 14, 1999; however, the application was abandoned. See also Weaver et al. U.S. 6,267,883, which is based on the Walker Alloy and the Panther Product and is identical to the Da-Gator and the Panther Products.
Spencer, U.S. Pat. No. 4,820,422, discloses a surface unit for countering scale formation in fluid conduits utilizing a metal alloy. The disclosure uses a series of alloy balls within a container and specifies that the device may be used in oil and gas production piping and in water piping. Spencer points out that an alloy rod has been used in the past but that the rod coated and lost its effectiveness. The ball arrangement supposedly causes the balls to rub against each other and help keep the balls clean.
As Spencer states, after the passage of time, the actual alloy tends to cake over and the effectiveness of the alloy is reduced. Spencer attempts to rectify the problem; however, the other devices make no attempt to “self-clean” the alloy. In fact, it is known that the alloy must be taken out-of-service and physically cleaned in order to maintain the efficiency and efficacy of the alloy.
None of the above devices are suitable for use in industrial conditions, nor do the devices assure turbulent mixing of the fluid passing through the device. (Spencer states that pressure drop is deliberately reduced.) Thus, there remains a need for an industrial fluid device that assures turbulent flow over the alloy and is easily maintained. Further, the device must meet certain safety standards (when used in critical flow conditions) and be relatively easy to manufacture.
The invention consists of a basket filter designed to be placed in the flow piping of a wellhead, water injection system, or recirculating process. The basket filter contains a basket liner and an insert containing the same alloy described in the Walker U.S. Pat. No. 4,789,031 patent. The design of the basket and insert is such that fluid is forced through the basket and insert in turbulent flow coming into general contact with the alloy. In contacting the alloy the electrostatic potential of the fluid is modified. The modification thereby causes solid minerals and certain hydrocarbons to be better suspended within the fluid. The improvement in suspension inhibits the formation of scale, or paraffin or corrosion in associated piping.